Electromagnet.



W. C. REED.

ELECTROMAGNET. 7 APPLICATION FILED FEB. 12. r913.

1,165,904. Patented Dec. 28, 1915.

I UNITED STATES PATENT OFFICE.

WALTER C. REED, 0F DALTON, MASSACHUSETTS, ASSIGNOR TO THE TELELECTRIC COMPANY, OF PITTSFIELD, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

ELECTROMAGNET.

T 0 all whom it may concern.

Be it known that I, WVALTER C. REED, a citizen of the United States, residing at Dalton, in the county of Berkshire and State of Massachusetts, have invented new and useful Improvements in Electromagnets, of which the following is a specification.

The object of my invention is to provide an improved key-operating magnet for use in electrically-operated piano players. If

such a magnet is to be thoroughly efficient it must be capable of operating within the time interval available for sounding a very short note, which may be less than a sixth of a second, and since the notes must be sounded sometimes loudly and sometimes softly it is highly important for the armature of the magnet not only to commence its movement very quickly but also to be subsequently accelerated at a rate varying with the strength of the current, the loudness of a given note being closely proportional to the interval of time occupied by the downward movement of the key. My invention provides a playing magnet having the qualities above referred to, together with certain other useful qualities such as economy in the consumption of current and the capacity for noiseless action, all of which are secured by certain features of construction and arrangement hereinafter described in connection with the accompanying drawing, in which Figure 1 is a side elevation illustrating my magnet as preferably constructed; Fig. 2 is a front elevation of the same; Fig.3 is a horizontal section on the line w-w in Fig. 1; Fig. 4 is a side elevation of the poles and 1 armature of the magnet illustrated in Fig.

-1, with the armature in its normal position; and Fig. 5 is a view similar to Fig. 4 but showing the armature in the position which it preferably occupies when the piano key to which it is connected is depressed.

The magnet illustrated in the drawing is of the horse-shoe type and comprises a soft iron core 2 having its arms surrounded by coils 3, with its poles 1 and 5 projecting somewhat beyond said coils and having their inner or opposed faces 6 and 7 formed on concave curves, as hereinafter described. The soft-iron armature of the magnet is shown at 8, and preferably it and the core Specification of Letters Patent.

Patented Dec. 28, 1915.

Application filed February 12, 1913, Serial N 0. 747,922.

2 are of laminated construction, in which case the several laminae may be punched from sheet metal by dies having the outline shown, and secured together side by side by suitable rivets 9.

The armature 8 is mounted to rock on a pivot 10 carried by non-magnetic brackets 11 riveted to the sides of the poles 4 and 5 but preferably held at a short distance therefrom by spacing pieces 12, and when the magnet is applied to a piano it is secured in such position that its core 2 and armature 8 occupy a vertical plane, so that the pivot 10 is horizontal. In the construction illustrated said pivot is so located that the upper portion of the armature, through which the pivot passes, always remains beneath the adjacent pole 4, or mainly so, and the opposed faces of the pole 4 and the armature are formed on conforming curves so plotted that there is provided between said pole and armature a gap 13 which varies in width as the armature rocks on its pivot, being closed in proportion as the lower end of the armature swings toward the lower coil 3. Preferably the curves just referred to are spiral curves having the pivotal axis of the armature as their center and of such nature that the width of the gap 13 will always be uniform throughout its length, whatever that width may be. At its lower end the armature 8 has an end face which conforms and is adapted to move in close proximity to the concave face 7 of the pole 5, both of these faces being formed on circular curves having the pivot 10 as their center of curvature, and when no current is flowing through the magnet coils the armature occupies a slanting position, as shown in Fig. 1, in which it is held by springs 14 against a felt-covered stop 15 carried by the brackets 11. In this position of the armature the gap 13 is open to the maximum extent and the lower end of the armature is located beyond the extremity of the pole 5, or mainly so, thus bringing said extremity in proximity to the pointed tip of a rearwardly-projecting portion 16 formed on the lower end of the armature.

Provision is made for connecting the armature 8 to a corresponding piano key by suitable means such as a coupling 17 pivotally mounted between arms 18 extending forward from the armature, said coupling being perforated to receive the lower end of a pull wire 19 connected at its upper end to the under side of the piano key in the usual manner. The wire 19 is clamped in the coupling 17 by a set screw 20 after the connections between the armature and the key have been so adjusted that when said key is in its normal or uppermost po sition the armature is held against the stop 15 as above described. In order that the armature may be readily disconnected from the fixed parts of the magnet, if desired, the ends of the pivot 10 are preferably located in notches formed in the froift edges of the brackets .11 and are held therein by clips 21 removably attached to the top of said brackets, as shown in Fig. 2.

The mode of operation of the magnet above described is as follows: Under normal conditions, that is, when no current is passing through the magnet coils and the armature is in the position represented in Figs. 1 and 1, the magnetic circuit has a low inductance due to its high reluctance, which exists mainly at the gap 13 and at the point where the extremity of the lower pole 5 and the pointed portion .16 of the armature are held in proximity to each other. Hence when the magnet is energized the magnetism builds up very quickly, since the time required therefor varies with the inductance of the magnetic circuit (the winding and the current strength being regarded as constant factors). Owing to the limited transverse area of the iron circuit at the extremity of the lower pole 5, however, the armature and pole are incapable of transmitting at this point all the initial magnetism developed, and the result is a concentrated magnetic stress which exerts a strong pull on the lower end of the armature and therefore gives it a quick start. As the armature moves toward the pole 5 the gap 13 grows narrower, and since the magnetic lines of force transmitted through this gap increase in inverse ratio to the square of the gap, the pull on the armature continuously increases through the movement of the latter. This pullis also substantially proportional, in any given position of the armature, to the strength of the energizing current, and the effect obtained, therefore, is quickness in the starting of the armature, coupled with a pull which varies with the current strength but always increases sufficiently, as the armature moves, to accellerate the piano key according to the force with which the note is to be struck.

The parts above described are preferably so proportioned and combined wlth the piano key that the gap 13 1s never completely closed, even when the key is fully depressed, since this sub ects the full downward movement of the key to the control of the armature and renders the latter effective to continue its pull upon the key throughout the striking movement of the latter.

While the various parts of my magnet preferably have the specific form and arrangement above described, it is to be understood that the same may be considerably modified in various ways without departing from my invention, which is broadly characterized by the provision of an electromagnet in which the magnetic circuit has an initially high reluctance, and the armature of which is subjected to a locally concentrated magnetic stress when the magnet is first energized and thereafter to a progressively increasing pull varying with the strength of the energizing current.

I claim:

1. An electro-magnet provided with an armature having one of its ends located mainly beneath one pole of the magnet in all positions of the armature and having its other end normally located mainly beyond the other pole of the magnet but movable over the same under the pull exerted thereby.

2. An electro-magnet having two poles and a pivotally-mounted armature provided with end faces formed respectively on spiral and circular curves having the pivotal axis of the armature as their centers, said poles being shaped to conform to the adjacent end. faces of the armature.

3. An electro-magnet having two poles and a pivotally-mounted armature providing a gap of variable width between one of its ends and the opposed face of the corresponding pole, the other end of said armature being movable along the face of the other pole in proximity thereto and provided with a pointed portion projecting laterally into proximity to the tip of the latter pole when the armature is in normal position.

4. An electro-magnet comprising two poles and a pivotally-mo-unted armaturehaving an end face located mainly beneath the opposed pole face in all positions of the armature, said faces being formed on curves adapted to provide between them a gap 1ntersecting the magnetic circuit and having a substantially constant area and a width which varies as the armature turns on its pivot.

5. An electro-magnet comprlsing two poles and a pivotally-mounted armature having an end face located mainly beneath the opposed pole face in all positions of the armature but separated therefrom by a gap, the width of which varies as the armature turns but is uniform throughout the length of the gap in any position of said armature.

6. An electro-magnet having two poles and a pivotally-mounted armature one end of which is normally located mainly beyond the corresponding pole and is provided with a pointed portion projecting laterally into proximity to the tip of said pole, the other with opposed faces, brackets secured to the sides of said poles and having transverselyalined notches in their front edges, a pivot having its ends located in said notches, means for removably holding said pivot therein, an armature carried by said pivot, and a stop carried by said brackets in position to limit the movement of said armature in one direction. I

In testimony whereof, I have hereunto subscribed my name this eighth day of February, 1913.

WALTER G. REED.

Witnesses:

PHILIP W. GOEWEY, F; G. STEVENS. 

